1. Field of the Invention
The present invention relates to a coating agent which is safe to use, which can be coated even in 100% water, which affords a finish that is not sticky despite its viscosity, thus resulting in coated particles that do not stick to each other, and which has an extremely low oxygen permeation coefficient, as well as to a novel, edible coating agent consisting of yeast cell wall fractions with the function of controlling dissolution time, coated materials comprising the use of such coating agents, and a coating film formed from such a coating agent.
2. Description of the Related Art
Fine particles, microcapsules, granules, tablets, and the like, comprising useful coated substances in a variety of forms or with various properties, such as colorless or colored dyes, medicinal products, agrochemicals, fragrances, feed materials, and food product materials, have conventionally been prepared for industrial purposes. Known examples of bases for coating fragrances, feed materials, food product materials, and the like, specifically, coating agents, include waxes and other oils, natural polysaccharides, proteins, shellac (natural resin secreted by the lac insect living in plants such as the legumes) and other resins, and the like. Chemically synthesized coating bases stipulated for medicinal additives are also known in the case of medicinal products.
Most of such conventionally known coating agents, however, suffer from the drawback of poor handling as a result of stickiness or poor dispersion during the preparation of the coating liquid. Additional problems with most medicinal additives such as shellac, zein (corn protein), and ethylcellulose, are their bad effects on the environment and their high cost because of the use of solvents such as ethanol have been indicated. Although water dispersion types of ethylcellulose-based coating agents have become commercially available recently, these also suffer from problems in terms of handling, such as the changes in solution properties depending on temperature conditions during storage, and the inability to release them in wastewater into rivers because they contain various solvents. Still another problem is the poor intestinal dissolution and the extremely slow dissolution speed of the aforementioned zein which can be used in the field of food products.
Attempts have meanwhile been made to develop film materials from yeast. Japanese Patent Publication (Kokoku) S56-19971, for example, discloses an edible protein film based on water-soluble proteins produced by removing the yeast cell membrane components from residual yeast which was produced by extracting nucleic acid. Japanese Laid-Open Patent Application (Kokai) S53-45385 discloses a method for producing a film, wherein the cells of a microorganism such as yeast are heated and alkali treated, acid is added for treatment involving isoelectric precipitation, the pH of the resulting precipitate is adjusted to between 6 and 8, and a plasticizer is added to the resulting gel-forming microorganism cells to produce a constituent.
Methods are also known for decoloring and deodorizing substances primarily comprising the cell walls left over in the form of residue during the extraction of yeast extract. Japanese Laid-Open Patent Application (Kokai) H4-248968, for example, discloses a method for decoloring and deodorizing yeast extract residue, wherein extract residue is treated with alkali and acid, is then treated with 1000 to 2000 ppm ozone, and is treated with ethanol before and after the ozone treatment. Japanese Laid-Open Patent Application (Kokai) H9-103266 discloses a method for eliminating the flavor and odor of a yeast autolytic insoluble substance, wherein a yeast autolytic insoluble substance is suspended in ethanol, and is stirred and treated in the presence of an alkali.
However, it has not been known that excellent use as a coating agent can be made, without additional chemical treatment, of yeast cell wall fractions consisting of yeast extract residue, for example, such as extract residue obtained after the components in soluble cells have been removed following the autolysis of live yeast cream at 40 to 50° C., or that further treatment of such yeast cell wall fractions with acidic aqueous solution affords a coating agent with better enteric properties allowing the time at which dissolution begins to be controlled.
That is, an object of the present invention is to provide a coating agent with an extremely low oxygen permeation coefficient, which remedies the drawbacks of conventional edible coating agents, for example, by having a finish that is not as sticky, despite its viscosity, as gums such as gum arabic, resins such as shellac, and zein or Eudragit, and which results in coated particles that do not stick to each other, as well as to a coating agent which can be used as an enteric coating agent capable of controlling the time at which dissolution begins.
In the course of research on yeast cell wall fractions occurring in the form of extract residue of yeast extract, particularly in the course of research on coating agents utilizing such yeast cell wall fractions, the inventors unexpectedly found that residue undergoing no ethanol treatment as described in Japanese Laid-Open Patent Applications H4-248968 or H9-103266, or any other chemical treatment during the treatment of the yeast extract residue had better film-formability, that is, film-forming properties, than that which had been treated with ethanol, and were particularly better as coating agents which require film properties, and that yeast cell wall fractions without any chemical treatment can be used as an unexpectedly excellent coating agent. Upon further research on such yeast cell wall fractions, the present invention was perfected when it was discovered that an excellent enteric coating agent capable of controlling the time at which dissolution begins was unexpectedly obtained using only acidic aqueous solution in varying concentrations, unlike conventional conditions for treating yeast with both alkali and acid treatments for deodorization and decolorization.